Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

An electrophoretic display device is constituted by a first substrate and
a second substrate which are disposed with a spacing therebetween, a
partition wall disposed in the spacing, electrophoretic particles sealed
in a closed space defined by the first and second substrates and the
partition wall, a first electrode disposed at a side surface of the
closed space, and a second electrode disposed at a bottom surface of the
closed space. In the electrophoretic display device, a distribution state
of the electrophoretic particles is changed to effect display, and the
first electrode has an area substantially equal to or larger than an area
of the second electrode.

Claims:

1.-11. (canceled)

12. An electrophoretic display device, comprising:a first substrate and a
second substrate which are disposed with a spacing therebetween,a
partition wall disposed in the spacing to define a closed space between
said first and second substrates,a plurality of first electrodes disposed
on a surface of said partition wall, which comprise a pair of first
electrodes on the surface of said partition wall at two opposite sides of
the closed space,a second electrode disposed at a surface of the second
substrate in the closed space, andelectrophoretic particles charged with
a polarity, said electrophoretic particles moving onto said plurality of
first electrodes by a first voltage application between said first and
second electrodes and moving onto said second electrode by a second
voltage application of an opposite polarity to the first voltage
application between the first and second electrodes,wherein a total area
of said plurality of first electrodes is equal to or larger than an area
of said second electrode.

13. An electrophoretic display device according to claim 12, wherein the
total area of said first electrodes is substantially not more than three
times the area of said second electrode.

14. An electrophoretic display device according to claim 12, wherein said
first electrodes are disposed at four sides of a rectangularly-shaped
closed space.

15. An electrophoretic display device according to claim 12, wherein the
closed space has a ratio of width to length of not less than 1:3 at a top
or a bottom surface thereof.

Description:

[0002]By remarkable development of an information technology, an amount of
varieties of information in society is increasing significantly.

[0003]In connection with this, needs of a display which is one of
information output apparatus are increasingly stronger, so that studies
on the display with respect to further improvements in definition, power
consumption, weight, and thickness have been conducted actively.

[0004]In recent years, of these displays which have been researched and
developed, electronic paper, which has a display quality equivalent to
printed matter and permits electrical writing and flexible portability,
has attracted attention. Further, the electronic paper is expected very
much also as a means for solving a forest environmental problem which is
in currently problematic due to mass consumption of paper. As one of
candidates of the electronic paper, an electrophoretic display apparatus
has been proposed by Evans et al. in U.S. Pat. No. 3,612,758.

[0005]The electrophoretic display apparatus includes an electrophoretic
display device constituted by a pair of substrates disposed with a
spacing therebetween, an insulating liquid filled in the spacing, colored
electrophoretic particles (charged migration particles) dispersed in the
insulating liquid, and a display electrode disposed along each of the
substrates.

[0006]The colored electrophoretic particles are electrically charged
positively or negatively, so that they are deposited on either one of the
display electrodes depending on a polarity of a voltage applied to the
display electrode. For example, the colored electrophoretic particles are
deposited on the upper (display) electrode to provide a visible state of
the colored electrophoretic particles or on the lower (display) electrode
to provide a visible state of the insulating liquid. Thus, display is
effected by utilizing a difference in color between the color of the
electrophoretic particles and the color of the insulating liquid which
has been dyed.

[0007]However, in such a conventional electrophoretic display device, when
writing only depending on a gradation value (level) on the basis of image
data is performed, a desired gradation value display cannot be effected
in some cases. This may be attributable to an influence of a DC component
remaining in the electrophoretic display device.

[0008]Hereinbelow, the influence of the residual DC component will be
described.

[0009]FIG. 9 shows an embodiment of a structure of a conventional
electrophoretic display device.

[0010]The electrophoretic display device includes: a dispersion liquid
comprising positively charged black electrophoretic particles 11,
negatively charged white electrophoretic particles 12, and an insulating
liquid in which the black and white electrophoretic particles 11 and 12
are contained; Electrodes, comprising a first electrode 15 and a second
electrode 16, for forming an electric field in the dispersion liquid by
applying a voltage between the electrodes; an insulating layer 17 for
separating the dispersion liquid 10 and the first electrode 15; an
insulating layer 18 for separating the dispersion liquid 10 and the
second electrode 16; and a partition wall for partitioning adjacent
pixels.

[0011]In the electrophoretic display device of this type, a relaxation
time constant of accumulated electric charges by drive of respective
parts is different depending on physical properties of respective
constitutional members. In the following description, the relaxation time
constant is defined as a product of an electric resistance and an
electrostatic capacity (capacitance) of each part when an equivalent
electric circuit is considered on the basis of an electric field
generated by each part. For example, the relaxation time constant of the
dispersion liquid 10 is a product of a resistance and a capacitance of
the dispersion liquid 10, thus being in agreement with a product of a
volume resistivity and a dielectric constant of the dispersion liquid 10.
When charges, such as ions contained in the dispersion liquid 10,
accumulate at the insulating layer surface, a time constant at the time
of discharging through the dispersion liquid 10 is determined by the
above defined relaxation time constant.

[0012]When a time constant τ1 of a dispersion liquid portion and a
time constant τ2 of an insulating layer portion satisfy τ1
<<τ2, ions are accumulated (deposited) on either one of the
upper and lower insulating layer surfaces depending on a polarity thereof
in the case of continuously applying a voltage of one polarity, so that
the charges are not readily attenuated due to the larger τ2. As a
result, the charges are also left even at both ends, of the insulating
layer portion, at which the charges are generally less liable to remain.

[0013]In this case, thereafter, even when the voltage applied between the
electrodes is made 0 V, the insulating layer portion also has a longer
charge relaxation time, thus leaving the charges thereat for a long time.
As a result, in spite of the fact that the voltage of 0 V is applied
between the electrodes, an internal voltage due to the residual charges
is generated upper and lower ends of the dispersion liquid portion. This
internal voltage is a residual DC voltage. By the residual DC voltage, a
voltage different from the applied voltage is applied between the upper
and lower ends of the dispersion liquid portion to cause display image
burning (burn-in).

[0014]Further, by such a phenomenon, in the case of performing a writing
operation by reference to only information on an image to be displayed, a
desired voltage cannot be applied to the electrophoretic particles 11 and
12. As a result, a desired display state cannot be obtained. More
specifically, in drive of the electrophoretic display device by applying
one-polarity voltage, i.e., a positive voltage or a negative voltage, a
DC component remains in the electrophoretic display device, so that there
arises such a problem that a voltage applied at the time of writing and
an effective voltage applied to the electrophoretic particles 11 and 12
are different from each other.

[0015]Further, in such a case where the electrophoretic display device is
driven to provide a low optical response speed and cause visual
recognition of reset display by a user, a base color of the electronic
paper is white, so that the electrophoretic display device is strongly
required to permit writing from white display reset. However, in the case
where the writing from white display reset is performed in a conventional
horizontal movement-type electrophoretic display device, a gradation
optical level is changed with respect to a minute fluctuation in drive
voltage, so that the electrophoretic display device is accompanied with
such a problem that gradation control is difficult.

[0016]Hereinbelow, the cause of this will be explained. For example, in a
conventional horizontal movement-type electrophoretic display device
shown in FIG. 10, at the time of white display reset, black
electrophoretic particles 11 are deposited in a plurality of layers on a
partition wall 7A provided with a first electrode 4A. An interparticular
attraction force determined by values of surface energy of the
electrophoretic particles 11 and the dispersion liquid 10 is weaker than
an attraction force, exerted between the electrophoretic particles 11 and
the partition wall 7A, determined by values of surface energy of the
electrophoretic particles 11, the dispersion liquid 10, and the partition
wall 7A.

[0017]Accordingly, the state in which the electrophoretic particles 11 are
deposited in the plurality of layers is unstable, so that the deposition
state is changed by a slight change in electric field strength
(intensity). As a result, an optical response characteristic in writing
from white display reset is changed abruptly. In other words, the
particles deposited state is changed even by the slight change in
electric field strength to unstabilize a resultant optical response
characteristic.

DISCLOSURE OF THE INVENTION

[0018]A principal object of the present invention is to provide an
electrophoretic display device having solved the above described
problems.

[0019]A specific object of the present invention is to provide an
electrophoretic display device capable of alleviating accumulation of
residual DC component and stabilizing an optical gradation level in
writing from white display reset.

[0020]According to an aspect of the present invention, there is provided
on an electrophoretic display device, comprising:

[0021]a first substrate and a second substrate which are disposed with a
spacing therebetween, [0022]a partition wall disposed in the spacing,
electrophoretic particles sealed in a closed space, defined by the first
and second substrates and the partition wall, in which a distribution
state of the electrophoretic particles is changed to effect display,

[0023]a first electrode disposed at a side surface of the closed space,
and

[0024]a second electrode disposed at a bottom surface of the closed space,

[0025]wherein the first electrode has an area substantially equal to or
larger than an area of the second electrode.

[0026]In the electrophoretic display device of the present invention, the
first electrode disposed at a side surface of the closed space and the
second electrode disposed at a bottom surface of the closed space have
the substantially same area, whereby it becomes possible to perform such
a drive that an opposite polarity voltage is alternately applied between
the respective electrodes even in the case of repetitively performing
display rewriting, thus alleviating remarkably the accumulation of the
residual DC component. Further, by providing the first electrode with a
larger area than that of the second electrode, it is possible to
stabilize an optical gradation level in writing from white display reset.

[0027]These and other objects, features and advantages of the present
invention will become more apparent upon a consideration of the following
description of the preferred embodiments of the present invention taken
in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a perspective view showing a pixel structure of an
electrophoretic display device according to First Embodiment of the
present invention.

[0029]FIGS. 2(a) and 2(b) are sectional views each showing electric line
of force at each pixel of the electrophoretic display device.

[0030]FIGS. 3(a) and 3(b) are graphs each showing an electrooptical
characteristic of the electrophoretic display device.

[0031]FIG. 4 is a time chart for illustrating a drive sequence for
effecting bipolar reset.

[0032]FIG. 5 is a sectional view showing a pixel of an electrophoretic
display device according to Second Embodiment of the present invention.

[0033]FIG. 6 is a perspective view showing a pixel of an electrophoretic
display device according to Third Embodiment of the present invention.

[0034]FIG. 7 is a top view of the pixel of the electrophoretic display
device shown in FIG. 6.

[0035]FIGS. 8(a) and 8(b) are perspective view each showing pixel(s) of an
electrophoretic display device according to Fourth Embodiment of the
present invention.

[0036]FIG. 9 is a sectional view showing an embodiment of a structure of a
conventional electrophoretic display device.

[0037]FIG. 10 is a sectional view showing a state at the time of white
display reset in a conventional horizontal movement-type electrophoretic
display device.

BEST MODE FOR CARRYING TO THE INVENTION

[0038]Hereinbelow, embodiments of the electrophoretic display device
according to the present invention will be described with reference to
the drawings.

First Embodiment

[0039]FIG. 1 is a schematic perspective view showing a pixel structure of
an electrophoretic display device according to this embodiment.

[0040]Referring to FIG. 1, the electrophoretic display device includes a
pixel G, a first substrate 1, a second substrate 2 disposed opposite to
the first substrate 1 with a spacing therebetween, a partition wall 7 for
keeping the spacing between the first and second substrates 1 and 2 at a
predetermined distance and partitioning the pixel and an adjacent pixel,
a closed space defined by the first and second substrates 1 and 2 and the
partition wall 7, a liquid-phase forming electrophoretic dispersion
liquid 3 in which a liquid-phase dispersion medium and charged
electrophoretic particles (not shown) dispersed in the dispersion medium
are sealed, a second electrode 5 formed on the second substrate 2, and a
first electrode 4 formed at a surface of the partition wall 7.

[0041]The electrophoretic display device in the embodiment is a matrix
panel having 600×1800 pixels. Each pixel G has a height A of 20
μm, a width B of 40 μm, and a length (depth) C of 120 μm. The
first electrode 4 is formed at surfaces of a pair of partition wall 7
portions constituting a pair of opposite side surfaces. In this
embodiment, two opposite side surfaces of four side surfaces and a bottom
surface of the pixel G is coated with the electrodes (the first and
second electrodes 4 and 5).

[0042]As the second electrode 5, a 1.1 mm-thick glass substrate is used,
and the second electrode 5 is disposed at the pixel G. Each of the
respective electrodes 4 and 5 is surface-coated with an insulating layer
6. As the electrophoretic particles contained in the electrophoretic
dispersion liquid 3 which is sealed in the closed space are black
particles. As the dispersion medium contained in the dispersion liquid 3
isoparaffin is used and, as the electrophoretic particles, particles of
polystyrene-polymethyl methacrylate copolymer (resin) (particle size: 1-2
μm) containing carbon black are used. At each pixel G, a thin film
transistor (TFT) is formed and connected with a voltage application
circuit, thus constituting an electrophoretic display apparatus.

[0043]Incidentally, in the case where, as shown in FIG. 1, the first and
second electrodes 4 and 5 have the same depth dimension (length) C and
the first electrode 4 is divided into two portions which are formed at
opposite two surfaces of adjacent partition wall portions 7, an area of
the first electrode 4 means a sum of areas of these (first electrode) two
portions 4.

[0044]In this embodiment, the pixel G has a ratio of A (height):B (width)
of 1:2, so that the first electrode 4 and the second electrode 5 have the
same area.

[0045]In such a case where the area of the first electrode 4 is equal to
the area of the second electrode 5, as shown in FIG. 2(a), a distribution
of electric field strength is substantially symmetrical with respect to
the electrode surfaces of the first electrode 4 and the second electrode
5. In other words, at the respective electrode surfaces, the electric
field strength varies depending on a position and has a distribution but
a manner of the distribution from a maximum to a minimum on the first
electrode surface is substantially identical to that on the second
electrode surface.

[0046]More specifically, the electric field strength on the first
electrode 4 is stronger with a shorter distance from the first substrate
1 and is weaker with a longer distance from the first substrate 1. On the
other hand, the electric field strength on the second electrode 5 is
stronger at a portion closer to the partition wall 7 and is weaken at a
pixel center portion. The electric field strength is determined by a
distance from a bonding (contact) portion of the partition wall 7 and the
first substrate 1. Accordingly, as apparent from the ratio A:B of 1:2,
the distribution of electric field strength on the first electrode 4 is
substantially identical to that on 1/2 of the entire second electrode 5.

[0047]Actually, the first electrode 4 contacts the second substrate 2 but
the half of the second electrode 5 is connected with the other half of
the second electrode 5. For this reason, the distributions of electric
field strength on the first and second electrodes 4 and 5 are not
completely identical to each other. Ideally, these distributions are
completely identical to each other in such a state that both of the first
and second electrodes are extended infinitely. However, by the neglect of
a difference in state between the end portion of the first electrode and
the center portion of the second electrode, it can be said that both of
the electric field strength distributions are substantially identical to
each other.

[0048]FIG. 2(b) shows a distribution of electric field strength in the
case where the area of the first electrode 4 and the area of the second
electrode 5 are not equal to each other. In this case, on the first
electrode 4, the electric field strength is created relatively uniformly
but on the second electrode 5, the electric field strength becomes very
small at the center portion of pixel. As a result, distributions of the
electric field strengths on the first and second electrodes are not equal
to each other.

[0049]As shown in FIG. 2(a), the distribution of electric field strength
to be exerted on the electrophoretic particles is symmetrical with
respect to the electrode surfaces of the first and second electrodes, so
that a resultant electrooptical characteristic showing a relationship
between an optical characteristic (R) and an applied voltage (V) is as
shown in FIG. 3(a), thus being improved compared with an electrooptical
characteristic in the case of asymmetrical electric field strength
distribution (FIG. 2(b)) shown in FIG. 3(b).

[0050]Here, in the case of a conventional electrophoretic display device
having the electrooptical characteristic shown in FIG. 3(b), there is a
considerable difference in optical response characteristic between
writing from white display reset and writing from black display reset, so
that it is difficult to perform bipolar reset which effects
opposite-polarity resets alternately. However, in the case of the
electrophoretic-display device of the embodiment having the
electrooptical characteristic as shown in FIG. 3(a), the optical response
characteristic in writing from white display reset is substantially
identical to that in writing from black display reset, so that it is
possible to perform reset operation by alternately changing a polarity
between a positive side and a negative side at the same voltage amplitude
and perform writing at voltages of both of the polarities.

[0051]FIG. 4 is a time chart showing a drive sequence for effecting
bipolar reset of the electrophoretic display device of this embodiment.
In the case of effecting the bipolar reset, first, a voltage Vrw is
applied so as to effect white display reset and then an arbitrary
gradation is written. Next, a voltage Vrb is applied so as to effect
black display reset and then an arbitrary gradation is written. The
voltages Vrw and Vrb have the same amplitude but have opposite
polarities. By effecting opposite-polarity resets alternately, it is
possible to perform such a drive that a residual DC is less liable to
accumulate. As a result, it is possible to perform stable display
rewriting which is less liable to cause burn-in.

[0052]As described above, by providing the first electrode 4 and the
second electrode 5 with the same area, it becomes possible to equalize
the electric field strength exerted on the electrophoretic particles in
writing from white display reset to that in writing from black display
reset. As a result, it is possible to perform bipolar-voltage drive using
positive and negative voltages (of both polarities). Further, even in the
case of repeating display rewriting, it becomes possible to perform such
a drive that the respective electrodes are alternately supplied with
voltages of opposite polarities, so that accumulation of the residual DC
component can be remarkably alleviated compared with a conventional
monopolar-voltage drive and it is possible to remedy the burn-in problem.

[0053]Incidentally, there is substantially no problem even when the areas
of the first and second electrodes 4 and 5 are not strictly equal to each
other but substantially equal to each other so long as an optical
characteristic in writing from white display reset with a predetermined
gradation accuracy is identical to that in writing from black display
reset with the predetermined gradation accuracy.

Second Embodiment

[0054]FIG. 5 is a schematic sectional view of a pixel of an
electrophoretic display device according to this embodiment, wherein the
same reference numerals as in FIG. 1 represent the same or corresponding
portions.

[0055]In FIG. 5, black electrophoretic particles 11 are contained in an
electrophoretic dispersion liquid 3. In this embodiment, a pixel G has a
height (A) of 60 μm, a width (B) of 40 μm, and a length or depth
(C) of 60 μm (FIG. 1). In other words, in this embodiment, a length in
a height direction of the pixel G is longer than a length in a width
direction.

[0056]Here, in the conventional electrophoretic display device, as
described with reference to FIG. 10, the electrophoretic particles 11 are
deposited in the plural layers on a cell deposition surface at the time
of white display reset and the particle deposition state is charged by
the slight change in electric field strength, thus resulting in a problem
of unstable optical response characteristic.

[0057]On the other hand, in the electrophoretic display device of this
embodiment, the electrophoretic particles 11 at the time of white display
reset are deposited in a single layer on the cell deposition surface as
shown in FIG. 5 because of the larger height (A) of the pixel G.

[0058]When the electrophoretic particles are preset at the electrode
surface in such a state that they are deposited in the plurality of
layers, electrophoretic particles directly contacting the electrode have
a strong deposition force but electrophoretic particles located at an
upper portion of the plurality of layers thereof have a weak deposition
force, thus being suspended in the dispersion liquid by a slight
oscillation or shaking. In the conventional electrophoretic display
device, one of the causes of an unstable collected state of
electrophoretic particles on the partition wall compared with an extended
state of electrophoretic particles on the substrate may be attributable
to the deposition state of electrophoretic particles in the plural
layers.

[0059]On the other hand, in such a deposition state of electrophoretic
particles that the electrophoretic particles are deposited on the second
electrode in the single layer, i.e., without being overlies, the particle
deposition state is table and is less liable to be changed by the slight
change in electric field strength, so that the optical characteristic of
the electrophoretic display device is not largely changed by a slight
change in applied voltage. Accordingly, compared with the conventional
electrophoretic display device, the electrophoretic display device of
this embodiment can stabilize an optical gradation level in writing from
white display reset and improve a controllability in gradation writing
from the white display reset.

[0060]As described above, by providing the first electrode 4 with an area
which is larger than an area of the second electrode 5, the
electrophoretic particles 11 are placed in such a deposition state that
they are deposited in the single layer in white display reset. As a
result, it is possible to improve a gradation controllability in writing
from the white display reset.

[0061]Incidentally, when the first electrode 4 is provided with an
excessively large area, a height of the partition wall 7 for partitioning
adjacent pixels is also increased. As a result, a production process
becomes difficult and there arise problems of lowering in light
reflectance, viewing angle, etc. For these reasons, the area of the first
electrode 4 may preferably be not more than approximately three times the
area of the second electrode 5.

Third Embodiment

[0062]FIG. 6 is a schematic perspective view of a pixel of an
electrophoretic display device according to this embodiment, wherein the
same reference numerals as in FIG. 5 represent the same or corresponding
portions.

[0063]In FIG. 6, a pixel G has a height (A) of 10 μm, a width (B) of 40
μm, and a length or depth (C) of 40 μm, and four side surfaces and
a bottom surface of the pixel G are coated with electrodes. More
specifically, in this embodiment, at four side surfaces (including two
pairs of opposite surfaces), the first electrode 4 is disposed.

[0064]Here, in such a electrophoretic display device, as described above,
even when the first and second electrodes 4 and 5 are provided with the
same area, electric field strengths at points on the first and second
electrodes 4 and 5 which have the same distance from a contact line
(edge) between the first and second electrodes 4 and 5 are not accurately
equal to each other. For this reason, in this embodiment, by adjusting a
thickness of the insulating layer 6, the electric field strengths at the
points on the first and second electrodes 4 and 5 which have the same
distance from the contact line are made equal to each other.

[0065]For example, as shown in FIG. 7 which is a top view of the pixel G,
the thickness of the insulating layer 6 of the second electrode 5 is made
larger at four corners of the pixel G where the electric field strength
is stronger and made smaller at a pixel center portion where the electric
field strength is weaker, whereby it becomes possible to perform bipolar
drive at the same drive voltage.

[0066]Further, a distance from the first electrode 4 to the surface of the
insulating layer 6 thereon and a distance from the surface of the
insulating layer 6 thereon are made equal to each other, and when an
intersection line is taken as a line of intersection of an extended plane
of the first electrode surface and an extended plane of the second
electrode surface, a distance from the intersection line to an edge of
the first electrode surface closest to the intersection line and a
distance from the intersection line to an edge of the second electrode
surface closest to the intersection line are made equal to each other. As
a result, it is also possible to make the electric field strengths at the
points on the first and second electrodes having the same distance from
the edge line between the first and second electrodes, equal to each
other.

[0067]By adjusting so, the electric field strength exerted on the
electrophoretic particles is symmetrical with respect to the white
display reset and the black display reset. As a result, the optical
response characteristic is improved compared with the conventional one,
thus resulting in the above described electrooptical characteristic as
shown in FIG. 3(a). More specifically, the optical response
characteristics in writing from the white display reset and from the
black display reset are substantially identical to each other, thus
permitting the bipolar reset operation.

[0068]By effecting the above described sequence shown in FIG. 4, the
opposite-polarity reset can be performed alternately to realize such a
drive that the residual DC component is less liable to accumulate. As a
result, it is possible to effect stable display rewriting with less
occurrence of the burn-in.

[0069]Incidentally, in the case where the distance from the first
electrode 4 to the insulating layer 6 surface thereon (first distance)
and the distance from the second electrode 5 to the insulating layer 6
surface thereon (second distance) cannot be made equal, when these first
and second distances satisfy the relationship of: (first
distance)>(second distance), it becomes possible to effect the bipolar
drive at the same drive voltage (amplitude) by satisfying the
relationship: (electrode area of first electrode 4)<(electrode area of
second electrode 5).

[0070]On the other hand, when the first and second distances satisfy the
relationship of: (first distance)<(second distance), it becomes
possible to effect the bipolar drive at the same drive voltage
(amplitude) by satisfying the following relationship: (electrode area of
first electrode 4)>(electrode area of second electrode 5).

Fourth Embodiment

[0071]Each of FIGS. 8(a) and 8(b) is a schematic perspective view of a
pixel of an electrophoretic display device according to this embodiment,
wherein the same reference numerals as in FIG. 1 represent the same or
corresponding portions.

[0072]In FIGS. 8(a) and 8(b), a side surface electrode 8 for preventing an
electric field generated by a first electrode 4 and a second electrode 5
from adversely affecting adjacent pixels is disposed at opposite two side
surfaces of four side surfaces of a pixel G.

[0073]More specifically, in this embodiment, of the four side surfaces of
the pixel G, the side surface electrode 8 is disposed at opposite two
side surfaces and the first electrode 4 is disposed at other opposite two
side surfaces. These four side surfaces and a bottom surface of the pixel
G are coated with electrodes (the first and side surface electrodes 4 and
8 and the second electrode 5).

[0074]In this embodiment, the pixel G has a height (A) of 20 μm, a
width (B) of 40 μm, and a length (depth) (C) of 60 μm as shown in
FIG. 8(a), so that an areal ratio between the side surface electrode 8
and the first electrode 4 is 2:3.

[0075]When three pixels G, each having the size shown in FIG. 8(a),
capable of displaying red, green and blue are arranged as shown in FIG.
8(b), the influence of the side surface electrodes 8 can be reduced. As a
result, it becomes possible to perform drive of the electrophoretic
display device only by the first electrode 4.

[0076]Incidentally, by making the length (depth) (C) of the pixel G
longer, i.e., making the B:C ratio being not less than 1:3, an electrode
area of the first electrode 4 is not less than three times that of the
side surface electrode 8. As a result, the first electrode 4 is dominant
with respect to determination of a distribution of electric field in the
pixel G, so that the influence of the side surface electrode 8 in drive
of the electrophoretic display device is further reduced.

[0077]In the above describe embodiments, the first electrode 4 has a
substantially rectangular shape but may be a substantially triangular
shape or a substantially polygonal shape.

INDUSTRIAL APPLICABILITY

[0078]As described hereinabove, according to the present invention, it is
possible to provide a practical electrophoretic display device wherein
the first electrode disposed at a side surface of the closed space and
the second electrode disposed at a bottom surface of the closed space
have the substantially same area, whereby it becomes possible to perform
such a drive that an opposite polarity voltage is alternately applied
between the respective electrodes even in the case of repetitively
performing display rewriting, thus alleviating remarkably the
accumulation of the residual DC component. Further, by providing the
first electrode with a larger area than that of the second electrode, it
is possible to stabilize an optical gradation level in writing from white
display reset in the electrophoretic display device.

[0079]While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set forth
and this application is intended to cover such modifications or changes
as may come within the purpose of the improvements or the scope of the
following claims.